Rich-Field Achromats

Abstract

Are you a casual observer; someone who enjoys a quick look around the landscape during daylight hours, or the river of stars that litter the Milky Way at night? Are you an experienced observer who already owns a large telescope but wishes to have a small portable system that gives decent, low, and moderate power views of the Moon, planets, and brighter deep sky objects? Or are you also a birder on a budget? If your answer is ‘yes’ to one or more of these questions, then chances are you wouldn’t go wrong with a rich-field refractor. By ‘rich field’ we mean an achromatic refractor with a relatively small aperture and short focal ratio. Though there are a number of refractors with apertures less than 80 mm on the market, this chapter will concentrate on models with apertures of 80 mm or greater because this is about the minimum aperture most amateur astronomers would be happy using in the field. Of course, you can still see a great deal in the night sky with smaller instruments, especially if you know what you’re looking for, and smaller instruments are often used by naturalists and birders during daylight hours. But we’ll explore these ultra-small optical wonders in a later chapter.